MILLIONS OF CANDIDATES. “Although this work identifies millions of putative functional RNA structures, their exact functional nature remains largely uncharted. One way to achieve this is by clustering them into families based on their structural topologies, thus deriving function via homology—an approach that has been applied to smaller sets of RNA structures.”
http://nar.oxfordjournals.org/content/early/2013/07/11/nar.gkt596.full